A review of long drop tubes as a supplement/alternative to space experiments

The 100 meter high drop tube at the Marshall Space Flight Center has proven to be a viable facility for studies of containerless solidification. Advantages are that experiments are inexpensive and large numbers of specimens can be processed rapidly. It would not be unusual to run ten specimens in a day. Another significant advantage is that the undercooling behavior can be followed with sufficient sensitivity to easily detect the onset of recalescence and subsequent events.Disadvantages are the restrictions on specimen sizes and types of alloys that can be run in a microgravity environment. Practical specimen sizes range between 50 mg and 500 mg depending on the type of furnace being used. Refractory alloys can be processed in a vacuum (about 10^?5 torr) and therefore at microgravity. Non-refractory alloys demand an atmosphere (about 200 torr) to obtain appreciable undercooling before impact at the bottom of the tube. Under these conditions significant g forces result.Because of the present limitations of the 100 meter drop tube, the most definitive work has been done on niobium based alloys. Large amounts of undercooling have been observed routinely and the effects of undercooling on microstructure have been characterized in detail. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy have been used to determine types of phases, amounts of phases, and compositions of phases. It is clear, as would be expected, that the results bear some resemblance to rapid solidification processing by quenching. However, there are dissimilarities due to the uniqueness of solidification by deep undercooling without quenching in long drop tubes and accompanying recalescence effects.     

Determination of aerodynamic forces on satellites by theory and wind tunnel experiments

Theoretical and experimental aspects of satellite aerodynamics in free molecular flow have been studied. A FORTRAN-program package has been developed to calculate free molecular aerodynamic force and moment coefficients of general and special convex shapes, using an approximation of the surfaces by plane triangular elements.As a special case for concave bodies, the drag of a satellite of TD1A-similar shape has been investigated by an approximate theory and by wind tunnel experiments. Comparisons are made between experimental results, the approximate theory and exact theory.     

An Optimal Normalization Scheme

An attitude normalization scheme, based on quaternion updates' of the attitude matrix in a strapdown system, is presented which is optimal in the two-norm sense. Furthermore, the algorithm requires minimal computer time and memory load.     

IR-spectroscopy of ionosphere from stratospheric balloons

The radiation spectra of the ionosphere in the 4–5 μm region have been determined from stratospheric balloons by means of the specially elaborated method of the registration of angular and spectral distribution of the radiation. The radiation bands of 4.4 μm and 4.8 μm which have 0.1–0.2 erg cm^?2 sr^?1s^?1. brightness obtained in two flights, are identified with the vibration-rotation transitions of the ion NO⁺ (0 - 1) and the molecules N¹⁴N¹⁵ (0 - 1) and CO (0 - 1) and (3 - 2) from altitudes between 120 and 500 km.     

Vertical profiles of halocarbons in the stratosphere

Stratospheric air samples collected between 10 and 35 km altitude my means of a cryogenic sampler were analyzed by gaschromatography. Thus vertical profiles of source gases for halogen radicals were derived, such as CCl₄, CCl₃F, CCl₂F₂, CClF₃, CF₄, C₂F₃Cl₃, C₂F₄Cl₂, C₂F₅Cl, C₂F₆, CH₃Cl, CH₃CCl₃, CHF₂Cl, CH₃Br, CBrF₃, and CBrCl₂F. Systematic discrepancies between measured and modelled halocarbon profiles point to deficiencies of present one- and two-dimensional models. Measurements of fully halogenated hydrocarbons provide a tool for systematically studying these deficiencies and thus improving the models.     

Simulation of Permanent Magnet Generator/Rectifier Combination

Permanent magnet generators are often used as the pilot exciters of three-stage generating units to provide an efficient and reliable source of electrical power. No external power supply is then necessary, and the problems associated with brushwear and with arcing at the rubbing contacts are eliminated. A technique is presented here by which the performance of a permanent magnet generator, when combined with a rectifier-fed d.c. load at its output terminals, may be accurately and efficiently computed. The machine model takes into account the magnetization characteristic of the permanent magnet rotor and involves only parameters which can be determined from terminal measurements on the machine at standstill. Both computed and measured characteristics for an experimental machine are presented, and a comparison of these characteristics shows that the model can predict accurately all the major characteristics of the machine, as well as its detailed internal performance, when supplying a typical resistiveinductive load.     

Gravitational influence on binary alloy melt equilibria

Micro- and macrosegregation, the nonuniform redistribution of solute during solidification, are common to both casting and welding, processes of fundamental importance in materials engineering. In multicomponent crystal growth where solid/liquid density differences are appreciable gravity-induced separation can lead to significant spatial variations in resulting ingot composition. In fact, this phenomenon is also operative in liquid/liquid systems such as monotectic alloys exhibiting a liquid miscibility gap, where buoyancy-driven flows can result in a sometimes unwanted separation of phases upon cooling through the miscibility dome.     

Thermocapillary migration of bubbles and droplets

The migration of a droplet in a large liquid body possessing a uniform temperature gradient is analyzed in the creeping flow limit for small values of the Marangoni number (ε). The method of matched asymptotic expansions is used for the solution of the field equations. The migration velocity is calculated to 0(ε²) and the result reduces to that of Young, Goldstein and Block [10] in the limit of zero Marangoni number.     

Implications for Entry Level Test Professionals

This paper discusses the product and manufacturing trends that are currently impacting the testing function. In addition, since educational experiences relevant to testing is minimal at most universities, the impact of current and future trends in testing are noted.